The core part of a helicopter is its main rotor. One or more driving mechanisms actuate the main rotor via a transmission and a rotor mast pivotally supported in the housing of the transmission and on which the rotor head is fastened.
The main rotor, with its two and more rotor blades which around their longitudinal axis are adjustably connected with the rotor head, takes care not only for the lift but also for the propulsion. Flapping hinges, drag links, elastomer bearings, or torsional bars serve to hinge the rotor blades on the rotor head. To produce a lift, the rotor blades are collectively or synchronously adjusted around an angle formed with the plane of rotation. A propulsion is obtained by the cyclic control, that is, the angle of incidence of a rotor blade during one revolution of the rotor mast runs through a maximum and a minimum. The direction of flight determines the position of the extreme values.
The pilot of the helicopter controls the rotor blades via a swash plate or spider. A swash plate consists of one stationary part which, via a so-called fork, is fastened on the housing of a transmission in a non-rotatable, but axially, displaceable manner and tiltably in all directions relative to the rotor mast, and of a rotational part pivoted, via radial and axial bearings, against the stationary part. The rotatable part moves with the stationary part in the axial direction, performing at the same time tilting motions. It is fastened on the rotor head via one other fork.
The movement of the swash plate is transmitted via a lever mechanism to rotor blade holding fixtures on the rotor head and this mostly in a manner such that the angle of incidence of a rotor blade enlarges approximately with the angle of the swash plate to the rotor head.
The helicopter pilot adjusts the swash plate for the flying maneuvers via another lever mechanism. Parallel to the latter servomotors are often disposed which, on one hand, facilitate the control and, on the other, make possible superposed control that counteracts rotor blade forces that appear.
The available maximum speed of helicopters is limited by rotor induced oscillations and by the degree of effectiveness of the forward flying main rotor. Oscillations and degree of effectiveness and determined by not optimal angles of incidence of the rotor blades relative to the momentary direction and speed of the blower stream and of the dynamic behavior. To counteract the effects, it is more flexibly advantageous to control the angle of incidence of the blade. Flutters resulting from broken flow on the rotor blades can be controlled, for example, by interference suppressing regulators with the aid of band filters for the first torsion inherent frequency of the rotor blades. Noise and vibrations are reduced thereby and the degree of effectiveness, the same as the economy, are improved. In addition the pilot""s work load is reduced.
Two active control systems are basically known (paper No. III.6.3.1, Sixteenth European Rotorcraft Forum, Sept. 18th to 21st 1990, Glasglow xe2x80x9cDevelopment and First Tests of Actuators for Single-Blade Controlxe2x80x9d, Peter Richter, Hans-Dieter Eisbrecher, Valentin Kloeppel), namely, the higher harmonic control superposed on the control of the swash plate and whose actuators are arranged below the swash plate in the helicopter fixed system and the single blade control where, with each rotor blade, one actuator is associated in the rotary system between the rotatable part of the swash plate and the rotor blade holding fixtures.
In the higher harmonic control, highly frequent blade angle changes are transmitted via the swash plate to the rotor blades by actuators in the helicopter fixed system. For reasons of geometry, only certain frequencies can be transmitted thereby, namely, the so-called blade number harmonics and the immediately adjoining frequencies wherefore in a four-blade rotor the fourth, third, and fifth, the eighth, seventh and ninth, etc. harmonics of the rotor rotary frequency but not the second, sixth or tenth harmonics. The same applies to rotors having more than four blades.
In the single-blade control, there are no limitations as to the frequencies and signal shape, but production cost for the actuators in the rotary system is considerably greater on account of the additional centrifugal force loads and the energy and signal transmission from the helicopter fixed system to the rotary system. Besides, the possibility of individually controlling each actuator involves the danger that the rotor blades move at random in case of malfunction of the control system, which impairs the safety.
From DE 196 27 860 A1 are also known mixed systems in which one swash plate interacts with one or more individual hydraulic actuators between the swash plate and the rotor blades. The actuators lie outside the mast and the rotor head and are exposed to environmental influences. Furthermore, the centrifugal forces of the actuators lying in the load train load the control system. It is also possible that two swash plates interact with each other.
It is further known from U.S. Pat. No. 3,080,002 that a swash plate is situated in the closed rotor head and adjusting systems lead to the swash plate through the rotor mast or a supporting column coaxially situated therein and fixedly connected with a transmission housing. Thereby the swash plate and the control rods for the rotor blades are protected by the rotor mast and the rotor head without impairing the air flow. Additional hydraulic actuators are not provided.
DE 36 39 168 C2 shows a similar solution in which control rods are guided through an annular space between a supporting column and the rotor mast.
The problem on which the invention is based is, in a helicopter of the above mentioned kind with an individual control of the rotor blades, to protect the control devices and accommodate them less loaded by foreign influences.
According to the invention, the control rods and the actuators are supported on the rotor mast and/or rotor head. They individual engage for each rotor blade in a maximum lever which acts via a control rod upon a pivoted arm and thus adjusts the pitch of the rotor blade. The actuators of the additional adjustment system are structurally bound in the rotary system or, according to one development, integrated therein so that they are exposed to no wind loads and their centrifugal forces, control, mass and added loads can, for the most part, be directly absorbed by the rotor mast or rotor head which is designed for much heavier loads. The total weight can be reduced by utilizing the structural frame conditions.
The actuation system of the actuators and control rods is coupled, via the mixing lever without added loads, the individual control portions being variable on the mixing lever by the distances from each other of the pivoting axles. It is, in addition, convenient that the control rod engages on a mixing lever between the pivoting axle of the control rod and the pivoting axle of the actuator on a pivoting axle. It is advantageous here that the distance of the pivoting axle of the control rod to the pivoting axle of the control rods be smaller than the distance to the pivoting axle of the actuator. These features make electrically or hydraulically tuning possible and optimizing the controlling force and regulating distance as the adjustment principle selected requires.
According to one development of the invention, the control rod is adjustable in length so that the zero position of the pitch of the rotor blades be easily set. Alternatively to this, it is possible to provide between the shaft and the rotor blade an element of adjustable rotation to make possible the adjustment of the angle of incidence. Besides, it is convenient that the longitudinal axles of the actuators and of the control rods extend parallel to the axis of rotation of the rotor mast so that the centrifugal forces have no effect on the adjusting movement. Besides, the actuators fastened on the rotary system can be easily supplied by lines along the walls of the rotor mast.
Since the control elements, actuators and control rods and the swash plate are disposed within. the rotor mast or the rotor head or within a transmission, the eventually available lubricants and hydraulic fluids can be used for them. Furthermore, they are lodged in a space protected against erosion and corrosion.
In the specification and in the claims are described numerous features in association. The expert conveniently will also separately observe the combined features, according to the problem to be solved, and make logical added combinations with them.